Research Methods

For execution of our research agenda we employ various
experimental methods and theoretical routines, ranging from thin film deposition, the characterization of structural, electrical and optical properties
to device fabrication and characterization.

Our vision: From deposition to device

Thin Film Epitaxy and Deposition

In pulsed laser deposition (PLD), a ceramic target is ablated by pulses from a high power laser. From the developing plasma, particles are
deposited onto the heated and rotating substrate.
Using PLD we perform epitaxy of oxide and nitride thin films and heterostructures (quantum wells, superlattices, ...)
in material systems such as (Mg,Zn)O,
(In,Ga,Al)2O3, ZnFe2O3, La(Ni,Mn)O3, BiFeO3, BaTiO3 and TiN.
Using sputter methods (Kathodenzerstäubung) we deposit amorphous semiconductor thin films and thin films of copper iodide.
Also we use reactive sputtering for the creation of Schottky contacts on various oxide semiconductors.
With plasma-enhanced chemical vapor deposition (PECVD) we deposit insulators and dielectric layers
in the Si/SiOxNy system.
Using thermal evaporation we deposit metals (Au, Al, Ti, ...) for Ohmic and Schottky contacts. Also oxide
nanostructures are fabricated using carbo-thermal evaporation schemes.
More on pulsed laser deposition

Structural characterization is the first step after sample fabrication in order to understand the crystal phase, lattice constants and strain state of the thin films. Also surface roughness or complex morphology such as nanowire arrays or circuit patterns are important properties that are analyzed.
More on X-ray diffraction

The measurement and understanding of electrical properties is essential for the design and modelling of electronic devices. For this purpose we entertain various methods to investigate electrical properties such as conductivity, carrier density, carrier mobility, and impedance. Typically frequency- and temperature-dependent investigations are made for conclusive analysis. The results also give a feedback to sample fabrication for optimized doping schemes.
More on IV and CV characterization

Current-voltage and capacitance-voltage spectroscopy, also as a function of temperature.Photos

Temperature-dependent Hall effect for the measurement of carrier density and mobility (and carrier type from sign of Hall effect). Evaluation with single and double channel models and quantitative mobility spectrum analysis.

The characterization of optical properties of bulk material, thin films and nanostructures concerns
the determination of the complex dielectric function tensor with spectroscopic ellipsometry, the phonon modes
with Raman spectroscopy, and recombination properties using photoluminescence with spectral,
spatial, angular, polarization and time resolution. Also cathodoluminescence is used for hyper-spectral
imaging of thin films, nano- and microstructures. All methods can be recorded as a function of temperature.
More on spectroscopic ellipsometry

Photoluminescence is used to investigate radiative recombination channels in various materials
and structures.

cw-photoluminescence using various lasers, e.g. HeCd (325 nm), for excitation without particular
spatial resolution. Spectra are detected using various photomultipliers (GaAs, MCP) and CCDs and are
recorded as a function of excitation density and temperature.
PhotoKey publications

Micro-photoluminescence using various cw- and fs-lasers for excitation with high, diffraction-limited spatial resolution. Spectra
can be recorded angularly resolved (Fourier imaging) and time-resolved with a streak camera (Hamamatsu C5680/Jobin-Yvon iHR320).
PhotoKey publications

Cathodoluminescence is used to image lateral variations of the emission spectrum in
thin films, micro- and nanostructures. The sample temperature can be varied from liquid helium
up to room temperature.
PhotoKey publications

We fabricate various devices such as diodes, transistors, photodetectors and solar cells as well
as integrated circuits (inverters, ring oscillators, ...) using (multiple) lithographic steps.More on photolithography

Funding is provided through the FUGG/HbfG and EFRE schemes as well as several cooperative projects
and individual grants. Most of our research is within the
university's research profile area
"Complex Matter".